Electrowetting display element with radiation filter

ABSTRACT

An apparatus comprising an electrowetting display element comprising a radiation filter, a first support plate, a second support plate, a first fluid and a second fluid immiscible with the first fluid. The apparatus comprises at least one processor and at least one memory comprising computer program instructions operable to, with the at least one processor: determine, based on an input signal indicative of a characteristic of an input to the apparatus, that a predetermined condition for reduction of an exposure of the first fluid to incident light is satisfied; and, in response, generate an output signal to control the electrowetting display element to configure the first fluid in a retracted configuration with the first fluid at least partly overlapped by the radiation filter and with both the first fluid and the second fluid in contact with a surface of the first support plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 14/582,308,filed on Dec. 24, 2014, the entire contents of which are incorporatedherein by reference.

BACKGROUND

Display devices with a matrix of electrowetting display elements areknown to be controlled using the active matrix driving technique. Thisinvolves for example addressing rows of display elements consecutively,to apply a voltage for setting a desired fluid configuration of eachdisplay element of the row being addressed.

Active matrix driving is an efficient technique for driving a matrix ofnumerous display elements. However, for some driving requirements, itcan be considered a complex driving technique.

It is desirable to devise an improved system for driving electrowettingdisplay elements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows schematically an example display element;

FIG. 2 shows a plan view of the example display element;

FIG. 3 shows schematically an example of circuitry for driving a matrixof display elements;

FIG. 4 shows schematically a driving method example;

FIGS. 5A and 5B are flow diagrams of examples of a method of controllinga matrix of electrowetting display elements;

FIGS. 6 and 7 show schematically an example display element;

FIG. 8 shows schematically an example of a system; and

FIG. 9 shows schematically an example circuitry arrangement.

DETAILED DESCRIPTION

FIG. 1 shows a diagrammatic cross-section of part of an example of anelectrowetting display device 1, including a plurality of pictureelements or display elements 2, one of which is shown in the Figure andwhich may also be referred to as an electrowetting cell. The lateralextent of the display element is indicated in the Figure by two dashedlines 3, 4. The display elements comprise a first support plate 5 and asecond support plate 6. The support plates may be separate parts of eachdisplay element, but the support plates may be shared in common by theplurality of display elements. The support plates may include a glass orpolymer substrate 7 a, 7 b and may be rigid or flexible. The supportplates in some examples include further layers and/or structures thanillustrated, for example circuitry for controlling the display elements.Such features are not illustrated, for clarity.

The display device has a viewing side 8 on which an image or displayformed by the display device can be viewed and a rear side 9. In theFigure a surface of the first support plate 5, which surface is in thisexample a surface of the substrate 7 a, defines the rear side 9; asurface of the second support plate 6, which surface is in this examplea surface of the substrate 7 b, defines the viewing side; alternatively,in other examples, a surface of the first support plate may define theviewing side. The display device may be of the reflective, transmissiveor transflective type. The display device may be an active matrix drivendisplay device. The plurality of display elements may be monochrome. Fora colour display device the display elements may be divided in groups,each group having a different colour; alternatively, an individualdisplay element may be able to show different colours.

A space 10 of each display element between the support plates is filledwith two fluids: a first fluid 11 and a second fluid 12 at least one ofwhich may be a liquid. The second fluid is immiscible with the firstfluid. Therefore, the first fluid and the second fluid do notsubstantially mix with each other and in some examples do not mix witheach other to any degree. The immiscibility of the first and secondfluids is due to the properties of the first and second fluids, forexample their chemical compositions; the first and second fluids tend toremain separated from each other, therefore tending not to mix togetherto form a homogeneous mixture of the first and second fluids. Due tothis immiscibility, the first and second fluids meet each other at aninterface which defines a boundary between the volume of the first fluidand the volume of the second fluid; this interface or boundary may bereferred to as a meniscus. With the first and second fluidssubstantially not mixing with each other, it is envisaged in someexamples that there may be some degree of mixing of the first and secondfluids, but that this is considered negligible in that the majority ofthe volume of first fluid is not mixed with the majority of the volumeof the second fluid.

The second fluid is at least one of electrically conductive or polar andmay be water, or a salt solution such as a solution of potassiumchloride in water. The second fluid may be transparent; it may insteadbe coloured, white, absorbing or reflecting. The first fluid iselectrically non-conductive and may for instance be an alkane likehexadecane or may be an oil such as silicone oil.

“Electrically conductive” for example means that the second fluid iscapable of conducting electricity; for example an electrical current mayflow through the second fluid due to the flow of ions or electronsthrough the second fluid. “Polar” in examples means that the secondfluid comprises at least one compound (for example a liquid vehicle)having a molecule with a net dipole; i.e. that across the molecularstructure the molecule has an overall dipole moment, due to an electrondistribution, with at least one part of the molecule having a negativeelectrical charge and at least one different part of the molecule havinga positive electrical charge. Such dipole moments include permanentdipoles. The polarity is caused for example by the presence of one ormore atom to atom bond in the molecule, with for example one of theatoms being a heteroatom such as oxygen or nitrogen. For example, such apolar atom to atom bond is a bond between an oxygen (O) atom and ahydrogen (H) atom, i.e. an —O—H bond, which may be in some examples dueto the presence of at least one hydroxyl (—OH) group. The presence ofsuch bonds may cause hydrogen bonding between different molecules withinthe second fluid.

The first fluid may absorb at least a part of the optical spectrum. Thefirst fluid may be transmissive for a part of the optical spectrum,forming a colour filter. For this purpose the first fluid may becoloured by addition of pigment particles or a dye. Alternatively, thefirst fluid may be black, for example absorb substantially all parts ofthe optical spectrum, or reflecting. A reflective first fluid mayreflect the entire visible spectrum, making the layer appear white, orpart of it, making it have a colour.

The support plate 5 includes an insulating layer 13. The insulatinglayer may be transparent or reflective. The insulating layer 13 mayextend between walls of a display element. To avoid short circuitsbetween the second fluid 12 and electrodes arranged under the insulatinglayer, layers of the insulating layer may extend uninterrupted over aplurality of display elements 2, as shown in the Figure. The insulatinglayer has a surface 14 facing the space 10 of the display element 2. Inthis example the surface 14 is hydrophobic. The thickness of theinsulating layer may be less than 2 micrometers and may be less than 1micrometer.

The insulating layer may be a hydrophobic layer; alternatively, it mayinclude a hydrophobic layer 15 and a barrier layer 16 with predetermineddielectric properties, the hydrophobic layer 15 facing the space 10, asshown in the Figure. The hydrophobic layer is schematically illustratedin FIG. 1 and may be formed of Teflon® AF1600. The barrier layer 16 mayhave a thickness, taken in a direction perpendicular the plane of thesubstrate, between 50 nanometers and 500 nanometers and may be made ofan inorganic material like silicon oxide or silicon nitride.

The hydrophobic character of the surface 14 causes the first fluid 11 toadhere preferentially to the insulating layer 13, since the first fluidhas a higher wettability with respect to the surface of the insulatinglayer 13 than the second fluid 12. Wettability relates to the relativeaffinity of a fluid for the surface of a solid. Wettability may bemeasured by the contact angle between the fluid and the surface of thesolid. The contact angle is determined by the difference in surfacetension between the fluid and the solid at the fluid-solid boundary. Forexample, a high difference in surface tension can indicate hydrophobicproperties.

Each display element 2 includes a first electrode 17 as part of thesupport plate 5. In examples shown there is one such electrode 17 perelement. The electrode 17 is electrically insulated from the first andsecond fluids by the insulating layer 13; electrodes of neighboringdisplay elements are separated by a non-conducting layer NCL. In someexamples, further layers may be arranged between the insulating layer 13and the electrode 17. The electrode 17 can be of any desired shape orform. The electrode 17 of a display element is supplied with voltagesignals by a signal line 18, schematically indicated in the Figure.

The support plate 6 includes a second electrode 19, which may extendbetween walls of a display element or extend uninterruptedly over aplurality of display elements 2, as shown in the Figure. The electrode19 is in electrical contact with the conductive second fluid 12 and iscommon to all display elements. The electrode may be made of for examplethe transparent conductive material indium tin oxide (ITO). A secondsignal line 20 is connected to the electrode 19. Alternatively, theelectrode may be arranged at a border of the support plates, where it isin electrical contact with the second fluid. This electrode may becommon to all elements, when they are fluidly interconnected by andshare the second fluid, uninterrupted by walls. The display element 2can be controlled by a voltage V applied between the signal lines 18 and20. The signal line 18 can be coupled to a matrix of control lines onthe substrate 7 a. The signal line 20 is coupled to a display drivingsystem.

The first fluid 11 in this example is confined to one display element bywalls 21 that follow the cross-section of the display element. Thecross-section of a display element may have any shape; when the displayelements are arranged in a matrix form, the cross-section is usuallysquare or rectangular. Although the walls are shown as structuresprotruding from the insulating layer 13, they may instead be a surfacelayer of the support plate that repels the first fluid, such as ahydrophilic or less hydrophobic layer. The walls may extend from thefirst to the second support plate but may instead extend partly from thefirst support plate to the second support plate as shown in FIG. 1. Theextent of the display element, indicated by the dashed lines 3 and 4, isdefined by the center of the walls 21. The area of the surface 14between the walls of a display element, indicated by the dashed lines 22and 23, is called the display area 24, over which a display effectoccurs. The display effect depends on an extent that the first andsecond fluids adjoin the surface defined by the display area, independence on the magnitude of the applied voltage V described above.The magnitude of the applied voltage V therefore determines theconfiguration of the first and second fluids within the electrowettingelement. In other words, the display effect depends on the configurationof the first and second fluid in the display element, whichconfiguration depends on the magnitude of the voltage applied to theelectrodes of the display element. The display effect gives rise to adisplay state of the display element for an observer looking at thedisplay device. When switching the electrowetting element from one fluidconfiguration to a different fluid configuration the extent of secondfluid adjoining the display area surface may increase or decrease, withthe extent of first fluid adjoining the display area surface decreasingor increasing, respectively.

FIG. 2 shows a matrix of rectangular picture elements in a plan view ofthe hydrophobic surface 14 of the first support plate. The extent of thecentral picture element in FIG. 2, corresponding to the dashed lines 3and 4 in FIG. 1, is indicated by the dashed line 26. Line 27 indicatesthe inner border of a wall; the line is also the edge of the displayarea 24.

When a zero or substantially zero voltage is applied between theelectrodes 17 and 19, for example when the electrowetting element is inan off state, the first fluid 11 forms a layer between the walls 21, asshown in the FIG. 1. Application of a voltage will retract the firstfluid to a retracted configuration, for example any configuration of thefirst fluid where the second fluid adjoins part of the display area, forexample a retracted configuration with the first fluid contractedagainst a wall as shown by the dashed shape 25 in FIG. 1 or FIG. 2. Aretracted configuration of the first fluid may for example be with thesecond fluid adjoining 50% or more than 50% of the display area. Inother examples a retracted configuration of the first fluid is such thatat least 50%, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95%, at least 98%, approximately 100% or 100% of the first fluidis overlapped by a radiation filter such as that described in examplesherein. The controllable shape of the first fluid, in dependence on themagnitude of applied voltage, is used to operate the picture element asa light valve, providing a display effect over the display area 24. Forexample, switching the fluids to increase adjoinment of the second fluidwith the display area may increase the brightness of the display effectprovided by the element.

This display effect determines the display state an observer will seewhen looking towards the viewing side of the display device. The displaystate can be from black to white with any intermediate grey state; in acolour display device, the display state may also include colour.

FIG. 3 shows schematically features of an example of an electrowettingdisplay apparatus 31. In this example of a so-called active matrix drivetype the display apparatus includes a display driving system and thedisplay device 2. The display driving system includes a displaycontroller or controller 33, a display row driver 34 and a displaycolumn driver 35. Data indicative of display states of the displayelements, the display states for example representing at least part of astill image or video image, is received via an input line 36 to thedisplay driving system. The display controller includes a processor 37for processing the data entered via the input line 36. The processor isconnected to at least one memory 38. The display controller prepares thedata for use in the display device.

The at least one memory may store computer program instructions that areconfigured to cause the display apparatus to perform one or more of themethods of controlling a display device as described herein when beingexecuted by the processor. The computer program instructions may bestored on a computer program product including a non-transitorycomputer-readable storage medium.

An output of the processor 37 is connected by line 39 to the display rowdriver 34, which includes row driver stages 40 that transform signals tothe appropriate voltages for the display device 2. The driver stages 40therefore are an example of first row voltage signal generators. Rowsignal lines 41 connect the row driver stages to respective rows of thedisplay device 32 for transmitting the voltage pulses generated in thedisplay row driver to display elements in each row of the displaydevice, thereby providing a row addressing signal to each row of thedisplay device. In other words, one or more voltage pulses foraddressing one or more rows is transmitted over the row signal lines 41corresponding to the rows to switchable elements corresponding, forexample associated, respectively to the display elements in the one ormore rows. The display row driver 34 generates the voltage pulses usedfor addressing the rows of the display device, using information fromthe processor 37 to set a value of the pulse duration of the voltagepulses.

Another output of the processor 37 is connected by line 42 to thedisplay column driver 35, which includes column driver stages 43 thattransform signals to the appropriate voltages for the display device 32.Column signal lines 44 connect the column driver stages to the columnsof the display device 32, providing a column signal to each column ofthe display device.

The display controller 33 determines which rows are selected foraddressing and in which order. The selected rows may for example beconsecutively addressed by applying an addressing signal, in the form ofat least one voltage pulse, to each of these rows. In alternativeexamples, other addressing sequences are envisaged, for example a randomrow addressing sequence. In examples where the display elements of a roware connected to the same row signal line, addressing a row meansaddressing each display element of that row. When a display element isbeing addressed, the display element receives the column signal that isapplied to the column signal line to which the display element isconnected. The column signal for a display element is appliedsubstantially simultaneously with the voltage pulse used for addressingthe display element. Substantially simultaneously means for example thatthe column signal is present on the column signal line for at least theduration of the voltage pulse.

The display drivers may comprise a distributor, not shown in FIG. 3, fordistributing data input to the display driver over a plurality ofoutputs connected to the driver stages. The distributor may be a shiftregister, which may be considered a memory. FIG. 3 shows the signallines only for those columns and rows of the display device that areshown in the Figure. The row drivers may be integrated in a singleintegrated circuit. Similarly, the column drivers may be integrated in asingle integrated circuit. The integrated circuit may include thecomplete driver assembly. The integrated circuit may be integrated onthe support plate 5 or 6 of the display device. The integrated circuitmay include the entire display driving system. Such an arrangement maybe known as a “chip on glass” (COG) construction. In other examples a“chip on foil” (COF) construction may be used, where the column and/orrow divers may be integrated on a foil rather than on the support plate5 or 6, which foil is connectable to circuit lines of the support platefor driving the picture elements.

The display device 32 comprises a plurality of display elements arrangedin a matrix of n rows, where n may be ≥2, for example larger than one,with m columns, where m may be ≥2. The total number of display elementsin this example is n×m. FIG. 3 shows display elements for five rows,labelled k to k+4 and four columns labelled 1 to 1+3. The total numberof rows and columns for common display devices may range between a fewhundred and a few thousand. The display elements, also called pixels, ofcolumn 1 are labelled p to p+4. Each display element may have the sameconstruction as the display element 2 in FIG. 1. In other examples adisplay element may represent a sub-pixel.

FIG. 3 shows electrical elements of the display elements. Each displayelement of the display device 32 includes an active element in the formof one or more switchable elements. The switchable element may be atransistor, for example a thin-film transistor (TFT) 33, or a diode. Thedisplay elements are indicated each with a pixel capacitor Cp formed byelectrodes 17 and 19. A line connecting the electrode 19 of thecapacitor to ground is the common signal line 20 and the line connectingthe electrode 17 of the capacitor to the drain terminal of thetransistor is the signal line 18 shown in FIG. 1. The display elementmay include a capacitor Cs for storage purposes or for making theduration of the holding state longer or the voltage applied to theelement uniform across the display device. This capacitor is arranged inparallel with Cp and is not separately shown in FIG. 3. The columndrivers provide the signal levels corresponding to the input data forthe display elements. The row drivers provide the signals for addressingthe row of which the elements are to be set in a specific display state.In examples, addressing a row means applying a signal on the signal lineof the row that switches a transistor of each of the display elements ofthe row to a conducting state of the transistor. Each row of the n rowsof the display device is addressable by a signal such as a voltagepulse; the voltage pulse is applied to a switchable element of each ofthe display elements in the addressed row for switching the switchableelement.

The addressing of rows is part of the addressing of display elements inan active matrix display device. A specific display element is addressedby: applying a voltage pulse to the row in which the specific displayelement is located, thereby driving the row and in particular examples aswitchable element such as a transistor of each of the display elementsin the row to a conducting state; and in coordination with this drivingthe row, applying a voltage to the column in which the specific displayelement is located, thereby driving the column and the specific displayelement by applying the voltage to the specific display element. Theterms driver and driving element are used herein in examples to describean electronic circuit or component for providing an appropriate signalsuch as a voltage level or voltage pulse for driving a display element,row and/or column.

When the transistor of a display element receives at its gate a voltagepulse of its row addressing signal, the transistor becomes conductingand it passes the signal level of its column driver to the electrode 17of the electrowetting cell. In examples, a voltage pulse is a rapid,transient change in the voltage from a baseline value, for example a lowvoltage level, to a greater or smaller magnitude, for example a highvoltage level higher in magnitude than the low voltage level, followedby a rapid return, for example change, to the baseline value. The timeperiod between the two subsequent voltage changes of the voltage pulseis called a pulse duration. After the transistor has been switched off,so the transistor is no longer conducting, the voltage over the cellwill be substantially maintained until the transistor is switched onagain by the next row addressing signal for the display element. Thetime during which the transistor is switched off is called the holdingstate of the element. In this active matrix driving method theelectrodes of the electrowetting cells are connected to the drivingstages briefly at the start of a period during which they show a certaindisplay effect. During this connection, a voltage related to the desireddisplay effect is applied to the electrodes. After the display elementis disconnected from the driver stage, the voltage on the electrodes issubstantially maintained by one or more capacitors during the periodduring which the display element shows the display effect. The method iscalled ‘active’, because the display element contains at least oneactive element, for example a transistor.

In examples described herein, for example that described using FIG. 3, asystem comprises a matrix of m columns and n rows of electrowettingdisplay elements, such as those display elements described using FIGS. 1and 3. Such a system further comprises a column driving systemconfigured to transmit a column voltage signal to the electrode of eachof the electrowetting display elements of at least one selected row ofthe n rows to be driven; such a column driving system is for example asdescribed using FIG. 3 which comprises the display column driver 35,including the column driving stages 43. Such a system further comprisesa first row driving system configured to transmit a first row voltagesignal, for example a voltage pulse as described below, to theswitchable element associated with each respective one of theelectrowetting display elements of the selected row of the n rows; sucha first row driving system is for example as described using FIG. 3which comprises the display row driver 34, including the row driverstages 40.

In examples described herein, such a system further comprises a secondrow driving system which is configured to transmit a second row voltagesignal, for example a voltage pulse as described below, to theswitchable element associated with each respective one of theelectrowetting display elements of a plurality of rows of the n rows ofelectrowetting display elements. Further details of an example of such asecond row driving system will now be described using FIG. 3. It is tobe noted that whereas in examples the first row driving system is fordriving individual rows of the n rows, by selecting one row at a timefor driving, the second row driving system is configured for driving aplurality of rows for example simultaneously, for example substantiallysimultaneously within acceptable timing tolerances. In this way,multiple rows of electrowetting display elements can be driven togetherby the second row driving system. The plurality in some examples, suchas that of FIG. 3, comprises the n rows and therefore for example thesecond driving system may be configured to drive the n rows of theelectrowetting display elements simultaneously. Therefore, all rows maybe driven substantially simultaneously.

In examples, for example that of FIG. 3, an output of the processor 37is connected by line 50 to a further display row driver 52 whichincludes a row driver stage 54 that for example, similar to the rowdriver stage 40, transforms signals to an appropriate voltage for thedisplay device. In this example the row driver stage 54 outputs avoltage Vhigh corresponding to a high voltage level of a voltage pulsefor transmitting to each switchable element such as the TFT 33associated respectively with each electrowetting display element of theplurality of rows of the n rows.

In examples such as that of FIG. 3, an output of the row driver stage 54is connected by lines 57 for connecting the Vhigh voltage signal to thelines 41 connecting the display row driver of the first row drivingsystem to a respective row of switchable elements associated with theelectrowetting display elements of the respective row. In the example ofFIG. 3 the second row driving system is connected by the lines 57 to theswitchable elements associated with the electrowetting display elementsof each row of the plurality of the n rows. Therefore, in examples wherethe plurality of the n rows comprises all n rows, the output of thefurther display row driver 52 is connected to each switchable elementassociated respectively with an electrowetting display element of all nrows, for example via lines 41.

In examples, the second row driving system comprises at least oneswitchable element SE configured to selectively control transmission ofthe voltage pulse to the switchable elements associated with eachrespective one of the electrowetting display elements of the pluralityof rows of the n rows of electrowetting display elements. The at leastone switchable element may be a plurality of switchable elements, forexample a TFT or diode similar to those described previously, with onesuch switchable element being connected with a source terminal of theswitchable element to the output of the further display row driver and adrain terminal of the switchable element connected to the switchableelements associated with the electrowetting display elements. Thus, inexamples, each of a plurality of such switchable elements is associatedwith a respective one row of the n rows and is configured to selectivelycontrol transmission of the voltage pulse to the switchable elementsassociated with each respective one of the plurality of switchableelements of the respective one row. In this way, by selectivelyswitching the switchable elements of the second row driving system, thevoltage pulse of the second row driving system can be selectivelyapplied to the switchable elements associated with the electrowettingdisplay elements. In the example of FIG. 3, the at least one switchableelement of the second row driving system is a plurality of TFTs SE eachconnected by their source and drain terminals in a respective one of thelines 57 connecting the further display row driver output to theswitchable elements associated with the electrowetting display elements.The gates of each TFT SE is connected to a respective line 60. FIG. 3illustrates such a TFT for each row with the label SE and thecorresponding row label. For example, the TFT for row k+1 is labelled SEk+1. The

In examples, each switching element of the second row driving system,for example TFTs SE k to SE k+4, is controllable by selectively applyinga control signal, for example a voltage pulse as described in examples,to the gate terminal of each switching element. In dependence of thisapplied voltage pulse, the switchable elements such as the TFTs of FIG.3 can be switched to be conducting or not, therefore either permittingtransmission of a voltage signal from the output of the further displayrow driver 52, via an input and output of the switchable element, to theswitchable elements associated with the electrowetting display elements,or not permitting such transmission.

In examples, for controlling the switching of the switching elementssuch as TFTs SE k to SE k+4, the second row driving system is configuredto transmit a voltage pulse to each of the plurality of switchableelements associated respectively with a row of the n rows ofelectrowetting display elements, for selectively controllingtransmission of a voltage pulse to each of the plurality of switchableelements associated with a respective one of the electrowetting displayelements. In some such examples, for example as now described inrelation to FIG. 3, the second row driving system has a controller 58connected by lines 60 to each switchable element SE k to SE k+4,specifically to the gate terminal of each TFT of the second row drivingsystem. The controller 58 is connected to an output of the processor 37by a line 62. The processor 37 can therefore coordinate using the firstand second row driving systems in dependence on the required driving ofthe electrowetting display elements.

The at least one memory and computer program instructions are thereforeconfigured to, with the at least one processor, in examples selectivelyswitch operation of the system between a first operation mode using thefirst row driving system for controlling the transmitting by the columndriving system of the column voltage signal to the electrode of eachelectrowetting display elements of at least one selected row of the nrows, and a second operation mode using the second row driving systemfor controlling the transmitting by the column driving system of thecolumn voltage signal to the electrode of each electrowetting displayelement of the plurality of rows of the n rows, for example all of the nrows. For example, the first operation mode may be used when activematrix type driving is required, for example when each or many of theelectrowetting display elements are required to be switched to adifferent display state. The second operation mode may instead be usedwhen the electrowetting display elements of all of the rows of theplurality of n rows, for example all n rows, are required to be switchedto the same display state.

Examples of operation of the system will now be described. One suchexample is now given using FIG. 4 in relation to the example of FIG. 3.

FIG. 4 shows a diagram of an example method of driving the displayelements. The method displays images during a series of frames, forexample, an image is displayed within the duration of one frame. Duringa frame all display elements of a display device may be addressed; in amatrix all rows of the matrix of a display device are addressed during aframe. FIG. 4 shows two column signals V1 and V1+1 and five rowaddressing signals Vk . . . Vk+4 of the first row driving system as afunction of time t for two consecutive frames r and r+1. Frames r andr+1 correspond to operating using the first row driving system and framer+2 corresponds with operating using the second row driving system.Additional signals Vhigh and VSE are illustrated too, which correspondrespectively with the output of the further display row driver 52 andthe output of the controller 58 of the second row driving system. It isnoted that “1” on the Vhigh axis does not represent a voltage of 1 voltsbut instead represents a high voltage level and that “0” on the Vhighaxis in the present examples represents a low voltage level. Theduration of a frame or frame period is Tf. In examples, a frame periodTf is a pre-determined period for addressing the n rows of the matrix.In some examples the frame period is the period between consecutiveaddressing of the same row. The duration of the period may be fixed, forexample programmed, in the controller 33. In other examples a frameperiod may be controlled to be different from frame to frame, dependingfor example on the content being displayed, for example whether rapidchanges to the display effect are required, or not.

When row k is selected and addressed by a pulse on the row addressingsignal Vk, as shown at the start of frame r in FIG. 4, the transistor ineach display element of row k becomes conducting and the voltages oneach of the column signal lines 44 will be put on the electrode 17 ofeach display element in row k. Subsequently, the display column driver35 of FIG. 3 changes the voltages on the column signal lines to thevalues required for row k+1. When row k+1 is selected by a pulse on rowaddressing signal k+1, the voltages are put on the electrode 17 of FIG.1 of the display elements of row k+1. All n rows of the display devicewill in this example be selected consecutively in a similar manner inframe r. The process of selecting the rows starts again in the followingframe r+1.

In common display apparatuses the pulse duration of the voltage pulse ofthe row addressing signal, also called the gate period Tg or gate time,is such that the n rows of the display device can be addressed forexample consecutively within one frame period. Common displayapparatuses have therefore usually a pulse duration equal to or lessthan Tf/n. For example, addressing 1000 rows in a frame period of 20milliseconds requires a pulse duration of 20 microseconds or less.

During frames r and r+1 the switchable elements SE k to SE k+4 are notconducting, with the controller 58 not transmitting a voltage pulse tothe switchable elements, as indicated by the plot of VS_(E). Therefore,although in some examples the Vhigh output is not zero, but insteadcorresponds to the voltage level of a voltage pulse for switching theswitchable elements SE k to SE k+4, it is not transmitted to theswitchable elements associated with the display elements as theswitchable elements SE k to SE k+4 of the second row driving system arenot switched to be conducting.

For frame r+2 the first row driving system is not used for selectingwhich rows of electrowetting display elements are connected to thecolumn driving system. Instead the second row driving system is used. Inthis example, it is desired to switch all of the electrowetting displayelements to a display state with the first fluid retracted to aretracted configuration, for example to the brightest display statewhich the controller is configured to switch the display elements to.The position of the first fluid for each display element may thereforebe switched to that illustrated in FIG. 1 using dashed line 25.

Thus, in the example of FIG. 4, to switch the first fluid of eachdisplay element to the same configuration, for example the fullyretracted configuration the controller is configured to drive the firstfluid to, a voltage is applied by each column driving stagecorresponding to the desired display state. The controller 58 of thesecond row driving system outputs a voltage pulse to each of theswitchable elements SE k to SE k+4 for switching them to a conductingstate. Thus, whilst these switchable elements are switched to aconducting state, they allow the voltage signal from the further displayrow driver 52 to be transmitted to the switchable elements 33 associatedrespectively with the electrowetting display elements of the pluralityof rows, in this case all n rows. The duration of the voltage pulse, asshown in FIG. 4 in the plot of V_(SE) corresponds with the duration ofthe voltage pulse transmitted to the switchable elements associated withthe display elements, as illustrated in plots of Vk to V k+4. Thus, inthis way, the further row driver 52 in combination with the switchableelements SE k to SE k+4 and the controller 58 can be considered in thisexample to operate together as a second row voltage signal generator,for example a second row voltage pulse generator, with the duration ofthe voltage pulse from the controller 58 determining the duration of thevoltage pulse transmitted to the switchable elements associated with theelectrowetting display elements.

With each of the switchable elements associated with the displayelements receiving the voltage pulse from the second row driving system,for example simultaneously, the electrode of each display element of acolumn of the matrix is connected to the voltage level of thecorresponding column driving stage. Therefore, with each column drivingstage set to output the maximum voltage level for example, all displayelements can be switched to a desired display state corresponding withthe maximum voltage level. Where this display state corresponds with awhite display effect of the display elements, for example in a matrix ofred green and blue (RGB) display elements and with each display elementdriven to its brightest state, then all display elements may besimultaneously driven so the overall display effect is white. In otherexamples, depending on the display effect of individual displayelements, a different colour or display effect may be given with thedisplay element driven to its brightest state.

Once all display elements of all rows, or the display elements ofwhichever plurality of rows is driven by the second driving system, havebeen driven to the required display state, the second row driving systemneed not immediately transmit a further voltage pulse to the switchableelements associated with the display elements of the appropriate rows.This is illustrated in FIG. 4 by the zero voltage level for all voltagesexcept for Vhigh. The capacitance of the display elements holds theconfiguration of the fluids and therefore the display state for a periodof time. However, to avoid deterioration of the display effect overtime, it may be necessary for the second row driving system to drive therows again to re-apply the required column voltage level to the displayelement electrodes.

It will be appreciated that it is possible to use the first row drivingsystem to switch multiple or all of the electrowetting display elementsto the same display state. However, as this operates on active matrixdriving principles, each row driver stage is used which requires greaterpower demands as each row driver stage is addressed individually with acontrolling signal from the controller. Using a different row drivingsystem, such as the second row driving system described herein, whichuses a single driver stage, different from a driver stage of the firstrow driving system, is considerably more power efficient. Furthermore,although it is envisaged in further examples that one of the driverstages of the first row driving system could be used and connected fordriving each of the electrowetting display elements of a plurality orall of the n rows, the use of a separate dedicated driving stage in thesecond row driving system allows a more appropriately specifiedelectrical component to be selected, and hence more design freedom,rather than needing to identify a component for the first row drivingsystem which needs to fulfill the needs of driving one row of displayelements and all rows of the display elements for the second mode ofoperation. Such a dedicated driving stage may therefore be more powerefficient given its selection for the specific requirements.

In further examples, it is envisaged that instead of the plurality ofswitchable elements SE illustrated in FIG. 3, one such switchableelement SE may be used to control transmission of a voltage signal fromthe further row driver stage 54 to the switchable elements associatedwith the plurality of display elements. In such an example, an output ofthe further row driver stage 54 may be connected to the source terminalof the one switchable element SE and the drain terminal may be connectedvia multiple lines respectively to the row lines 41 k to 41 k+4. Thecontroller 58 in such an example would therefore be connected to thegate terminal of the one switchable element SE.

Although some examples of circuitry implementations are given, it is tobe appreciated that the functionality of the first and second rowdriving systems may be implemented in further circuitry implementationsnot described herein but readily understood by the skilled person.

Examples will now be described where the second mode of operation may beused. FIGS. 5A and 5B relate to examples of such examples.

First examples of using the second mode of operation are described withreference to FIGS. 6 and 7. FIGS. 6 and 7 show an example of a displayelement similar to that shown in FIGS. 1 and 2; the same referencenumerals are used to label the same features. Corresponding descriptionsfor such features should be taken to apply also.

The second support plate 6 in the example of FIG. 6 comprises at leastone layer. The at least one layer includes for example a colour filterCF, for example as a layer, and a layer comprising a radiation filter F,described in more detail below, and for example a planarisation layer Pfor filling the layer adjacent to the radiation filter F. The colourfilter CF absorbs at least one wavelength of light, for example in thevisible spectrum, thus filtering the light passing through the colourfilter to provide a coloured display state; this may be the case inexamples where the first fluid is black. The colour filter may be formedof a material having a colour filtering property, or may comprise alayer of a material transmissive for substantially all, for example 90%or more, wavelengths of light, in for example the visible spectrum, witha coating to act as the colour filter. The colour filter CF in theexample of FIG. 6 is positioned between the radiation filter F and thespace 10 and for example covers substantially all of the display area.In other examples, the colour filter CF may lie on top of the radiationfilter F, such that the radiation filter F is between the colour filterCF and the space 10. Further examples include a single filter elementwhich performs the function of the colour filter and the radiationfilter and thus is a combined colour and radiation filter; such examplesmay comprise a region which acts as the colour filter but not theradiation filter and a different region which acts as the radiationfilter but not the colour filter; in other examples a single filterelement may have a region which performs the function of both the colourfilter and the radiation filter, which may in some further examples bein addition to separate colour filtering and radiation filteringregions. The second support plate 6 in other examples does not include acolour filter, for example in cases where the first fluid 11 isappropriately coloured, for example due to the addition of a dye orpigment, for providing the colour of a display state.

In some examples, for example that being described using FIGS. 6 and 7,at least one of the first fluid 11 or the second fluid 12 aresusceptible to deterioration by exposure to radiation of at least onepredetermined wavelength. Deterioration may be any type of physical orchemical degradation, disintegration or decomposition of the first fluidand/or the second fluid, for example of a component of the first and/orsecond fluid. Exposure to radiation in examples refers to the radiationbeing incident on the first and/or second fluid, for example such thatthe first and/or second fluid are irradiated by the radiation. At leastone of the first fluid or the second fluid may be susceptible toexposure to radiation over a sustained or long period of time, forexample over a period of operation of the display device of a day ormore, either over one continuous period of time or over a plurality ofperiods of time with a total duration of a day or more. Alternatively,the at least one of the first fluid or the second fluid may besusceptible to exposure to short bursts of radiation, for example anhour or less.

In examples, at least one of the first fluid or the second fluidcomprises an additive which is susceptible to deterioration by exposureto the radiation of the at least one predetermined wavelength. Theadditive may be or comprise a fluid and/or solid particles, for example.The deterioration may be one or more of: a decomposition of theadditive, or, with the additive being a colourant, such as a dye or apigment as explained above, a change of colour of the colourant forexample due to a decomposition of the chemical structure of thecolourant. Such a change of colour may be a decolouring, for example ableaching, for example due to a photobleaching reaction on exposure toradiation. In examples, the decolouring may result in the colourantchanging to a different colour from its original colour. A change ofcolour of the colourant in examples reduces the amount of the colouranthaving the original, for example desired, colour. In such examples, theamount or concentration of the colourant with the original colour isreduced compared with an initial amount or concentration of colourant,resulting in decolouring.

In the example of FIG. 6, the second support plate 6 comprises a layercomprising a radiation filter F, for example a radiation filter layer,configured to filter input radiation, for example at least some, forexample at least a portion of the, radiation of the at least onepredetermined wavelength for which the at least one of the first fluidor the second fluid are susceptible to deterioration. For example, theradiation filter F in examples selectively blocks radiation of the atleast one predetermined wavelength, for example by absorbing orreflecting the radiation, such that radiation of the at least onepredetermined wavelength is not transmitted through the radiationfilter. In examples, some or all radiation with a wavelength which isnot one of the at least one predetermined wavelengths is transmitted orat least partly transmitted through the radiation filter. The radiationfilter is for example a layer which may have a substantially uniformthickness (“substantially” means for example within acceptablemanufacturing tolerance). As the skilled person will readily appreciate,the radiation filter in examples is formed of or comprises a suitablematerial or compound for filtering the at least one predeterminedwavelength, for example including a dye or a pigment or an organicmaterial; the specific material will depend on the specific wavelengthor range of wavelengths to be at least partially filtered. The radiationfilter in examples is formed of a non-fluid material, for example asolid plastic material which may be flexible or rigid. This non-fluidmaterial may have been formed by applying and then hardening orsolidifying a fluid material.

In examples, the at least one predetermined wavelength the at least oneof the first fluid or the second fluid are susceptible to deteriorationby is one or more of the following wavelengths: at least one wavelengthin the range of about 100 to about 380 nanometers, at least onewavelength in the range of about 380 to about 700 nanometers or at leastone wavelength in the range of about 700 nanometers to about 1000nanometers. The term “about” includes a degree of variation, thereforethe at least one wavelength may be within the range of wavelengthswithin acceptable measurement uncertainties, for example within 10% ofthe upper or lower bound of the range of wavelengths. In an example, theat least one predetermined wavelength is one or more of: at least onewavelength in the ultraviolet range of the electromagnetic spectrum, forexample within the range of 100 to 380 nanometers, at least onewavelength in the visible range of the electromagnetic spectrum, forexample within the range of 380 to 700 nanometers, or at least onewavelength in the infrared range of the electromagnetic spectrum, forexample within the range of 700 to 1000 nanometers. In an example, theradiation filter F filters radiation of a plurality of wavelengths, forexample a plurality of wavelengths within one or more of theultraviolet, visible or infrared ranges of the electromagnetic spectrum.In further examples, the radiation filter F filters ultraviolet andvisible radiation, ultraviolet and infrared radiation, visible andinfrared radiation or ultraviolet, visible and infrared radiation.

As the radiation filter F is positioned between the viewing side 8 ofthe display device 1 and the first 11 and second 12 fluids, theradiation filter F therefore prevents or reduces incident radiation ofthe at least one predetermined wavelength, for example ambient radiationwhich is incident on the second support plate 6 from the viewing side 8of the display device 1, from being transmitted from the side of theradiation filter F on which the radiation is incident, for example theside of the radiation filter F closest to the viewing side 8, to theother, for example opposite, side of the radiation filter F, for examplethe side of the radiation filter F closest to the second fluid 12. Thisprevents the parts of the first 11 and second 12 fluids which arebeneath, for example covered by, the radiation filter F from beingexposed, or for example irradiated, by the radiation of the at least onepredetermined wavelength. The parts of the first 11 and second 12 fluidswhich are protected from the radiation by the radiation filter F in thisway are therefore not deteriorated, or have a reduced deterioration, byexposure to the radiation whilst beneath the radiation filter. Thisimproves the lifetime of the display device 1 by increasing the usefullifetime of one or both of the first and second fluids.

To prolong the lifetime of one or both of the first and second fluids,it is therefore desirable to switch the configuration of the first andsecond fluids so that for example, whenever possible, as much of thefluid which is susceptible to deterioration is configured to be coveredby the radiation filter F. For example, if the first fluid issusceptible to deterioration, then wherever possible it is desirable toswitch the first and second fluids to a configuration with the firstfluid configured with the form indicated with label 25, so the radiationfilter F covers the first fluid. During operation of the display devicewhen showing content, for example text or a movie, configuring the firstfluid with the form as shown with label 25 may not be possible. However,during for example a period of inactivity of the display device, or forexample if incident light on the display element is detected as beingharmful to the lifetime of the first fluid, the display element, forexample a plurality or all of the display elements of the display devicemay be switched to a configuration of the first and second fluids withthe first fluid being at least partly, for example substantiallyentirely, or for example entirely, covered by the radiation filter F.

To switch a plurality of the display elements, for example a pluralityof the n rows, for example all n rows of the display elements to thisfluid configuration, it is more power efficient to use the second modeof operation for driving the rows than the first mode of operation.

Therefore, for example, the at least one memory and the computer programinstructions are configured to, with the at least one processor, measurea period of inactivity of the electrowetting display elements. Forexample, a period of inactivity may be identified if no input from auser to the device is received within a given timeframe, for example agiven duration of for example 30 minutes. Upon identifying such a periodof inactivity, the at least one memory and the computer programinstructions are configured to, with the at least one processor, switchoperation of the system from the first operation mode to a secondoperation mode. Then, once in the second operation mode, the displayelements of a plurality of the n rows, for example all of the n rows,may be driven to configure the first and second fluids so the firstfluid is configured to be covered at least partly, for examplesubstantially entirely as shown by label 25, by the radiation filter F,thus protecting the first fluid from incident light which maydeteriorate the first fluid. The display elements remain in this fluidconfiguration for a period of time after the voltage has been removedfrom the display element due to the capacitance of the display element.However, to maintain the configuration of the first and second fluidswith the first fluid configuration shown with label 25, in some examplesa further voltage is applied to each of the plurality of the n rows ofdisplay elements, for example all n rows, periodically using the secondrow driving system. Driving the plurality of the n rows, for example allof the n rows, for this purpose of protecting the first fluid againstdeterioration, using the second operation mode has less powerrequirements than using the first operation mode.

In some examples, in addition to, or alternative to, the measuring aperiod of inactivity as explained above, the system may include a lightsensor which for example detects an intensity of light incident on thesensor and/or a particular wavelength or range of wavelengths. The lightsensor is in examples positioned such that the detected light intensityand/or wavelength(s) is indicative of light incident on the displayelements and for example the first and second fluids. In examples, if adetected light intensity is measured as being above a predeterminedlight intensity threshold and/or of a predetermined wavelength or rangeof wavelengths, the at least one memory and the computer programinstructions may, with the at least one processor, in dependence on asignal from the light sensor which signal is for example indicative ofthe exceeding of the predetermined light intensity threshold and/or thepredetermined wavelength or range of wavelengths, switch theelectrowetting display device to the second mode of operation and forexample drive the plurality, for example all, of the n rows of displayelements to the fluid configuration shown in FIG. 6, so that in thisexample the first fluid is covered by the radiation filter F to prolongits lifetime.

In other examples, the second mode of operation may be used where thedisplay device is to display an image where many of the n rows ofdisplay elements are to have the same configuration of first and secondfluids. For example, the at least one memory and the computer programinstructions may be configured to, with the at least one processor,process input image data to identify where the display effect of aplurality of the n rows of display elements is to be the same. This mayfor example be the case where text is being displayed by the displaydevice; rows of display elements which are to provide a display effectfor providing for example a space, for example a white space, betweentextual characters, for example lines of text, being displayed bydifferent rows of display elements, may all be driven together, usingthe second mode of operation, to provide the white display effect. In afurther example, before displaying a new page of text to a user, thesecond operation mode may be used to drive a plurality, for example all,of the n rows of display elements to provide a display effect totemporarily blank the image displayed by the device, for example to awhite page display effect, before then driving the appropriate displayelements to display the text of the next page of text content to bedisplayed by the device. Using the second mode of operation to drive theplurality of n rows is more power efficient than the first mode ofoperation which required individually driving each of the row drivers ofthe first row driving system using the active matrix technique.

Further examples are envisaged where the second operation mode isuseful, as the skilled person will readily appreciate.

FIG. 8 shows schematically a system diagram of an example system, forexample apparatus 150, comprising an electrowetting display device suchas any of the examples described above, for example the electrowettingdisplay device described above comprising electrowetting displayelements 2. The apparatus is for example a portable, for example mobile,device such as an electronic reader device such as a so-called“e-reader”, a tablet computing device, a laptop computing device, amobile telecommunications device, a watch or a satellite navigationdevice; the apparatus may alternatively be a display screen forinstallation in any machine or device requiring a display screen, forexample a consumer appliance.

The system diagram illustrates an example of a basic hardwarearchitecture of the apparatus 150. The apparatus includes at least oneprocessor 152 connected to and therefore in data communication with forexample: a display device control subsystem 154, a communicationssubsystem 156, a user input subsystem 158, a power subsystem 160 andsystem storage 162. The display device control subsystem 154 isconnected to and is therefore in data communication with the displaydevice. The at least one processor 152 is for example a general purposeprocessor, a microprocessor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, a discrete gate ortransistor logic, discrete hardware components, or any suitablecombination thereof designed to perform the functions described herein.A processor may also be implemented as a combination of computingdevices, e.g., a combination of a DSP and a microprocessor, a pluralityof microprocessors, one or more microprocessors in conjunction with aDSP core, or any other such configuration. The processor may be coupled,via one or more buses, to read information from or write information toone or more memories, for example those of the system storage 162. Theat least one processor may additionally, or in the alternative, containmemory, such as processor registers.

The display device control subsystem 154 for example includeselectrowetting display element driver components, for use in applying avoltage to any of the electrowetting display elements, to addressdifferent such display elements. In examples the electrowetting displayelements are configured according to an active matrix configuration andthe display device control subsystem is configured to control switchingelements such as thin film transistors (TFTs) of the display device 1via circuitry to control the electrowetting display elements. Thecircuitry may include signal and control lines such as those describedabove.

The communications subsystem 156 for example is configured for theapparatus to communicate with for example a computing device via a datanetwork, for example a computer network such as the Internet, a localarea network, a wide area network, a telecommunications network, a wirednetwork, a wireless network, or some other type of network. Thecommunications subsystem 156 may further for example comprise aninput/output (I/O) interface, such as a universal serial bus (USB)connection, a Bluetooth or infrared connection, or a data networkinterface for connecting the apparatus to a data network such as any ofthose described above. Content data as described later may betransferred to the apparatus via the communications subsystem.

The user input subsystem 158 may include for example an input device forreceiving input from a user of the apparatus. Example input devicesinclude, but are not limited to, a keyboard, a rollerball, buttons,keys, switches, a pointing device, a mouse, a joystick, a remotecontrol, an infrared detector, a voice recognition system, a bar codereader, a scanner, a video camera (possibly coupled with videoprocessing software to, e.g., detect hand gestures or facial gestures),a motion detector, a microphone (possibly coupled to audio processingsoftware to, e.g., detect voice commands), or other device capable oftransmitting information from a user to the device. The input device mayalso take the form of a touch-screen associated with the display device,in which case a user responds to prompts on the display device by touch.The user may enter textual information through the input device such asthe keyboard or the touch-screen.

The apparatus may also include a user output subsystem (not illustrated)including for example an output device for providing output to a user ofthe apparatus. Examples include, but are not limited to, a printingdevice, an audio output device including for example one or morespeakers, headphones, earphones, alarms, or haptic output devices. Theoutput device may be a connector port for connecting to one of the otheroutput devices described, such as earphones.

The power subsystem 160 for example includes power circuitry 166 for usein transferring and controlling power consumed by the apparatus. Thepower may be provided by a mains electricity supply or from a battery164, via the power circuitry. The power circuitry may further be usedfor charging the battery from a mains electricity supply.

The system storage 162 includes at least one memory, for example atleast one of volatile memory 168 and non-volatile memory 170 and maycomprise a non-transitory computer readable storage medium. The volatilememory may for example be a Random Access Memory (RAM). The non-volatile(NV) memory may for example be a solid state drive (SSD) such as Flashmemory, or Read Only Memory (ROM). Further storage technologies may beused, for example magnetic, optical or tape media, compact disc (CD),digital versatile disc (DVD), Blu-ray or other data storage media. Thevolatile and/or non-volatile memory may be removable or non-removable.

Any of the memories may store data for controlling the apparatus, forexample components or subsystems of the apparatus. Such data may forexample be in the form of computer readable and/or executableinstructions, for example computer program instructions. Therefore, theat least one memory and the computer program instructions may beconfigured to, with the at least one processor, control a display effectprovided by the electrowetting display device.

In the example of FIG. 8, the volatile memory 168 stores for exampledisplay device data 172 which is indicative of display effects to beprovided by the display device. The processor 152 may transmit data,based on the display device data, to the display device controlsubsystem 154 which in turn outputs signals to the display device forapplying voltages to the display elements, for providing display effectsfrom the display device. The non-volatile memory 170 stores for exampleprogram data 174 and/or content data 176. The program data is forexample data representing computer executable instructions, for examplein the form of computer software, for the apparatus to run applicationsor program modules for the apparatus or components or subsystems of theapparatus to perform certain functions or tasks, and/or for controllingcomponents or subsystems of the apparatus. For example, application orprogram module data includes any of routines, programs, objects,components, data structures or similar. The content data is for exampledata representing content for example for a user; such content mayrepresent any form of media, for example text, at least one image or apart thereof, at least one video or a part thereof, at least one soundor music or a part thereof. Data representing an image or a part thereofis for example representative of a display effect to be provided by atleast one electrowetting element of the electrowetting display device.The content data may include data representing a library of content, forexample a library of any of books, periodicals, newspapers, movies,videos, music, or podcasts, each of which may be represented by acollection of data which represents for example one book or one movie.Such a collection of data may include content data of one type, but mayinstead include a mixture of content data of different types, forexample a movie may be represented by data including at least image dataand sound data.

FIG. 9 shows schematically features of an example of an implementationof the first and second row driving systems. Features describedpreviously are labelled with the same reference numerals andcorresponding descriptions should be taken to apply here also. In thisexample, on a surface of the substrate 7 of the first support platewhich surrounds the display elements 2, circuitry for the second rowdriving system is mounted. This circuitry for example includes circuitlines and the switchable elements of the second row driving system. Thecircuitry may be divided into two parts, labelled in FIG. 9 as 66 a and66 b, with one part 66 a connected to the switchable elements associatedwith display elements of odd numbered rows and the other part 66 bconnected to the switchable elements associated with display elements ofeven numbered rows. This circuitry and the electrodes of the displayelements are connected to the appropriate drivers and other circuitrysuch as the processor 37 which are mounted on a separate substrate 64from the substrate 7. This example allows the second row driving systemto be implemented in a compact manner. In other examples, at least someof the circuitry mounted on the separate substrate 64 shown in FIG. 9 isinstead mounted on the substrate 7, for a more integral circuitryimplementation.

The above examples are to be understood as illustrative examples.Further examples are envisaged. For example, in examples above thelabels row and column have been used to refer to lines of displayelements with a particular orientation; it is envisaged that in furtherexamples features described above in relation to a row may insteadrelate to a column and features described above in relation to a columnmay instead relate to a row. It is to be understood that any featuredescribed in relation to any one example may be used alone, or incombination with other features described, and may also be used incombination with one or more features of any other of the examples, orany combination of any other of the examples. Furthermore, equivalentsand modifications not described above may also be employed withoutdeparting from the scope of the accompanying claims.

What is claimed is:
 1. An apparatus comprising: a light sensorconfigured to generate an input signal indicative of a characteristic ofan input to the apparatus, wherein the characteristic is acharacteristic of light detected by the light sensor; an electrowettingdisplay element comprising: a radiation filter; a first support plate; asecond support plate; a first fluid; and a second fluid immiscible withthe first fluid, the first fluid and the second fluid located betweenthe first support plate and the second support plate; at least oneprocessor; and at least one memory comprising computer programinstructions operable to, with the at least one processor: receive theinput signal from the light sensor; determine, based on the inputsignal, that a predetermined condition for reduction of an exposure ofthe first fluid to incident light is satisfied; and, in response,generate an output signal to control the electrowetting display elementto configure the first fluid in a retracted configuration with the firstfluid at least partly overlapped by the radiation filter and with boththe first fluid and the second fluid in contact with a surface of thefirst support plate.
 2. The apparatus according to claim 1, comprising:a matrix of m columns and n rows of electrowetting display elements,wherein m and n are integers and the electrowetting display element islocated in a first column of the m columns and in a first row of the nrows; column driving circuitry; and row driving circuitry, wherein theoutput signal comprises a column voltage signal and a row voltage signaland the computer program instructions are operable to, with the at leastone processor, and in response to the predetermined condition forreduction of the exposure of the first fluid to the incident light beingsatisfied: transmit the column voltage signal to the first column usingthe column driving circuitry; and transmit the row voltage signal to thefirst row using the row driving circuitry, to control the electrowettingdisplay element to configure the first fluid in the retractedconfiguration.
 3. The apparatus according to claim 2, wherein theelectrowetting display element comprises: a first electrode located inthe first support plate; a second electrode in contact with the secondfluid, the second fluid being at least one of: electrically conductiveor polar; and a switchable element, wherein the column driving circuitryis configured to transmit the column voltage signal to the firstelectrode, the column voltage signal having a first magnitude forconfiguration of the first fluid in the retracted configuration, and therow driving circuitry is configured to transmit the row voltage signalto the switchable element, the row voltage signal having a secondmagnitude for switching the switchable element to a conductive state. 4.The apparatus according to claim 1, wherein the light sensor is locatedrelative to the electrowetting display element to receive ambient lightindicative of a characteristic of light incident on the electrowettingdisplay element.
 5. The apparatus according to claim 1, wherein: thecharacteristic is an intensity of the light; the predetermined conditionis a predetermined intensity condition; and the computer programinstructions are operable to, with the at least one processor, processthe input signal to determine that a magnitude of the intensity of thelight satisfies the predetermined intensity condition; or thecharacteristic is a wavelength of the light; the predetermined conditionis a predetermined wavelength condition; and the computer programinstructions are operable to, with the at least one processor, processthe input signal to determine that a wavelength of the light satisfiesthe predetermined wavelength condition.
 6. The apparatus according toclaim 5, wherein: to determine that the magnitude of the intensity ofthe light satisfies the predetermined intensity condition, the computerprogram instructions are operable to, with the at least one processor,determine, based on the input signal, that the magnitude of theintensity equals or exceeds a predetermined intensity threshold; or todetermine that the wavelength of the light satisfies the predeterminedwavelength condition, the computer program instructions are operable to,with the at least one processor, determine, based on the input signal,that the wavelength is: a predetermined wavelength; or within apredetermined range of wavelengths.
 7. The apparatus according to claim6, wherein the predetermined range of wavelengths is at least one of:about 100 nanometers to about 380 nanometers; an ultraviolet range of anelectromagnetic spectrum; about 380 nanometers to about 700 nanometers;a visible range of the electromagnetic spectrum; about 700 nanometers toabout 1000 nanometers; or an infrared range of the electromagneticspectrum.
 8. The apparatus according to claim 1, wherein the radiationfilter is configured to at least partly filter, from input radiation,radiation of at least one predetermined wavelength which at least one ofthe first fluid or the second fluid is susceptible to deteriorationfrom.
 9. The apparatus according to claim 1, wherein the radiationfilter is at least one of: a non-fluid radiation filter, a substantiallysolid radiation filter, or a substantially solid plastic radiationfilter.
 10. The apparatus according to claim 1, wherein the radiationfilter is positioned between a viewing side of the electrowettingdisplay element and at least one of the first fluid or the second fluid.11. The apparatus according to claim 1, wherein, with the first fluid inthe retracted configuration, the first fluid is substantially entirelyoverlapped by the radiation filter.
 12. The apparatus according to claim1, wherein one of the first support plate or the second support platecomprises a layer comprising a first region comprising the radiationfilter and a second region free from the radiation filter, wherein, withthe first fluid in the retracted configuration, the second regionsubstantially non-overlaps the first fluid.
 13. The apparatus accordingto claim 1, comprising a plurality of the electrowetting displayelement, wherein the computer program instructions are operable to, withthe at least one processor: configure the first fluid of each of theplurality of the electrowetting display element in the retractedconfiguration, on the basis that the predetermined condition issatisfied.
 14. The apparatus according to claim 1, wherein the computerprogram instructions are operable to, with the at least one processor,switch the first fluid from a non-retracted configuration, with thesecond fluid not in contact with the surface of the first support plate,to the retracted configuration, wherein a larger part of the first fluidis overlapped by the radiation filter with the first fluid in theretracted configuration than with the first fluid in the non-retractedconfiguration.
 15. A method of controlling an electrowetting displayelement, the method comprising: determining that a predeterminedcondition for reduction of an exposure of a first fluid of theelectrowetting display element to incident light is satisfied, theelectrowetting display element comprising a second fluid immiscible withthe first fluid, the first fluid and the second fluid located between afirst support plate of the electrowetting display element and a secondsupport plate of the electrowetting display element; and, in response,configuring the first fluid in a retracted configuration with the firstfluid at least partly overlapped by a radiation filter of theelectrowetting display element and with both the first fluid and thesecond fluid in contact with a surface of the first support plate,wherein the method comprises at least one of: detecting an intensity oflight using a light sensor, wherein the determining that thepredetermined condition is satisfied comprises determining that amagnitude of the intensity of the light satisfies a predeterminedintensity condition; detecting a wavelength of light using a lightsensor, wherein the determining that the predetermined condition issatisfied comprises determining that the wavelength of the lightsatisfies a predetermined wavelength condition; or measuring a measuredduration of a period of inactivity of the electrowetting displayelement, wherein the determining that the predetermined condition issatisfied comprises determining that the measured duration of the periodof inactivity of the electrowetting display element satisfies apredetermined duration condition.
 16. The method according to claim 15,wherein the radiation filter is configured to at least partly filter,from input radiation, radiation of at least one predetermined wavelengthwhich at least one of the first fluid or the second fluid is susceptibleto deterioration from.
 17. The method according to claim 15, comprisingconfiguring the first fluid of each of a plurality of the electrowettingdisplay element in the retracted configuration, on the basis that thepredetermined condition is satisfied.
 18. An apparatus comprising: anelectrowetting display element comprising: a radiation filter; a firstsupport plate; a second support plate; a first fluid; and a second fluidimmiscible with the first fluid, the first fluid and the second fluidlocated between the first support plate and the second support plate; atleast one processor; and at least one memory comprising computer programinstructions operable to, with the at least one processor: determine,based on an input signal indicative of a measured duration of a periodof inactivity of the electrowetting display element, that apredetermined condition for reduction of an exposure of the first fluidto incident light is satisfied; and, in response, generate an outputsignal to control the electrowetting display element to configure thefirst fluid in a retracted configuration with the first fluid at leastpartly overlapped by the radiation filter and with both the first fluidand the second fluid in contact with a surface of the first supportplate.
 19. The apparatus according to claim 18, wherein the computerprogram instructions are operable to, with the at least one processor,determine that the measured duration of the period of inactivity of theelectrowetting display element equals or exceeds a predeterminedduration.
 20. The apparatus according to claim 18, wherein the computerprogram instructions are operable to, with the at least one processor,generate the input signal, the input signal indicative of a measuredduration of a period within which no data indicative of a display statefor display by the electrowetting display element is received by the atleast one processor.
 21. The apparatus according to claim 18, whereinthe radiation filter is configured to at least partly filter, from inputradiation, radiation of at least one predetermined wavelength which atleast one of the first fluid or the second fluid is susceptible todeterioration from.